Jimmy is a 17-year old student at Titan High School (Teitan High School in the original version) and is already a well-known detective. He dreams of being a great detective like Sherlock Holmes and gets his dose of reality from his childhood friend Rachel Moore (Ran Mori in the original Japanese). Jimmy's parents, Booker and Vivian (Yusaku and Yukiko) live in the United States while Jimmy lives in Japan.

After solving a murder at the theme park Tropical Land, Jimmy witnessed an exchange between an unknown man and another person in all black. He is so focused on the exchange (an blackmail over an arms deal) that he does not notice an accomplice sneak behind him. This accomplice, another man in all black, hits him at the head and gives him a newly manufactured poison. This poison APTX 4869 was designed to kill a person and leave no traces of itself. However, instead of killing Jimmy, it slowly shrunk his body, making him appeared to be six or seven years old. He found the only person who may believe his story; his next door neighbor, close family friend, and eccentric scientist Dr. Agasa. Jimmy convinces Dr. Agasa that he was shrunk and was determined to discover who and what the men in black are. However, Dr. Agasa convinces him that in order to keep his identity secret lest the Black Organization would come back and kill him for real, as well as anybody who knew Jimmy was still alive. So Jimmy fashioned an alias, Conan Edogawa (Edogawa Conan) , after Arthur Conan Doyle and Edogawa Rampo. "Conan" goes to live with Rachel and her father, Richard Moore (Kogoro Mori), a private detective. Jimmy hopes that by living with a detective, he can stay on top of current cases and be able to gather hints about the "Black Organization". Unfortunately, Detective Moore is so incompetent that Jimmy often has to solve the mysteries for him.

Jimmy, as Conan, isn't taken as seriously as a child, so he has to improvise. Jimmy frequently knocks out Detective Moore with a dart shooting watch and uses his voice-changing bow tie to imitate Moore. Because of this, Moore gets the credit. Cases begin to pile up and Moore's reputation grows, occasionally giving Jimmy a chance to gather hints on the Black Organization.

Because Jimmy expects himself to return to his original form soon, he never tries to convince anybody that he is dead. As a matter of fact, knowing that Rachel misses Jimmy, Conan calls her over the telephone and imitates Jimmy's voice so that she is not worried about him. He convinces her that he is off solving a very difficult mystery-- which is not false-- and will return once the investigation concludes.

Due to striking similarities between Conan and Rachel's memories of Jimmy as a child, Rachel often suspects Conan is Jimmy, but every time she does, Conan does something childish to make her ignore the idea. Larger schemes, created by Jimmy or his friends, has been used to convince Rachel that Conan is not Jimmy. This usually follows an extremely story arcs. In such srcs Conan tends to drop his guard in order to save someone or to fully investigate a crime.

In more recent of the stories, Rachel becomes really sure of Conan's true identity and ask him to admit the truth. Sometimes, Jimmy felt he cannot trick her anymore. Jimmy got close to telling, but then something happens, like a person talks to him about it or someone pretends to be Jimmy while Conan is there. After his first encounter with Harley Hartwell (Heiji Hattori), Conan discovers the poison that was fed to him could temporarily be deactivated through drinking alcohol. He made this discovery when he temporarily turned back into Jimmy after Harley gave Conan some Chinese liquor as some kind of cold remedy. This is one of the two occasions where Jimmy turned back into his full form. This cure however, only works once.

Following Jimmy's transformation and her own transformation using Chinese liquor, Ai Haibara manages to create a temporary cure for Jimmy which lasted 24 hours in book 26 of the manga. Jimmy solves a case (under his own identity) and managed to bring Rachel out for dinner during this period of time. He had to "leave for an important case" during the dinner, and Conan returned.

Due to the unstable characteristics of the temporary cure, it is highly possible to die from taking it. Thus Jimmy has only taken the cure once so far, and that was under desperate circumstances. It is not known whether this temporary cure works only once like the Chinese liquor which Jimmy ingested previously, or works every time. Ai also mentioned a "time lag" to Jimmy once, which suggests that the temporary cure may not work for exactly 24 hours all the time.

People knowing Conan's identity include Dr. Agasa, the Kudo couple (Booker and Vivian), Harley Hartwell, Ai Haibara, Vermouth, and Phantom Thief Kid. (Only in the movies, and there is no description about him knowing it in the original manga.) Both Akemi Miyano (Ai Haibara's elder sister) and Hiroki Sawada (a character in Detective Conan: The Phantom of Baker Street) learned Conan's secret before they died.

Conan befriends three other children, Amy Yeager (Ayumi Yoshida), George Kojima (Genta Kojima), and Mitch Tsuburaya (Mitsuhiko Tsuburaya). Together they form the Junior Detective League (Detective Boys or Shonen Tantei in Japanese).